Method and apparatus for process control in time division multiplexed (TDM) etch process

Abstract

The present invention provides a method for controlling pressure in a vacuum chamber during a time division multiplexed process. A throttle valve is pre-positioned and held for a predetermined period of time. A process gas is introduced into the vacuum chamber during the associated plasma step (deposition or etching) of the silicon wafer. At the end of the predetermined period of time, the process gas continues to flow with the throttle valve being released from the set position. At this point, the throttle valve is regulated through a proportional derivative and integral control for a period that lasts the remaining time of the associated plasma step.

Description

CROSS REFERENCES TO RELATED APPLICATIONS[0001]This application claims priority from and is related to commonly owned U.S. Provisional Patent Application Ser. No. 60 / 460,932, filed Apr. 7, 2003, entitled: A Method and Apparatus for Process Control in Time Division Multiplexed (TDM) Etch Processes, this Provisional Patent Application incorporated by reference herein.FIELD OF THE INVENTION[0002]The present invention generally relates to the field of semiconductor wafer processing. More particularly, the present invention is directed to a method and apparatus for controlling the reaction chamber pressure during a time division multiplexed etching and deposition process.BACKGROUND OF THE INVENTION[0003]The fabrication of high aspect ratio features in silicon is used extensively in the manufacture of micro-electro-mechanical (MEMS) devices. Such features frequently have depths ranging from tens to hundreds of micrometers. To ensure manufacturability, the etching processes must operate at ...

AI Technical Summary

Benefits of technology

The present invention provides a method and apparatus for controlling pressure in a vacuum chamber during a TDM process. The method includes steps of regulating the pressure by setting a throttle valve at a predetermined position for a predetermined period of time to ensure that the chamber pressure does not overshoot or undershoot the desired operating level. The method also includes introducing a process gas into the chamber and enabling a closed loop pressure control algorithm to control the pressure at a recipe specified pressure set point for the remaining time of the process. The invention allows for an anisotropic etching process with improved accuracy and efficiency.

Problems solved by technology

However, as described earlier, the inability to control pressure during the transition of the constantly alternating TDM process steps is the real issue, and cannot be addressed by Kessel's technique.

Additionally, many TDM processes employ alternating process steps which last only a few seconds or shorter, which makes pressure control impractical using the disclosed technique.

However, in many TDM processes, changing process gas flow rate during a process step is undesirable.

Beyer does not teach how to use this technique in TDM processes.

While Puech teaches the control of pressure in the TDM processes that employ process steps on the order of one second, the method does not teach the use of actively regulating throttle valve in pressure control.

The current methods of pressure control for TDM processes, Pressure Control and Position Control, have limitations.

One problem with pressure control mode in a TDM process is that, in practice, there is typically a trade off between achieving fast pressure response time while minimizing set point deviations.

A problem with the current method of Position Control mode in a TDM process is unacceptably long pressure response times. While position mode minimizes process overshoot, the slower response times result in the chamber pressure spending a large fraction of the process time approaching the requested set point value (i.e., out of compliance with the recipe specified set point).

Another problem with the position control mode method is that it is an open loop pressure control algorithm.

Therefore, there is not any correction for perturbations in gas flow or pumping efficiency.

These perturbations tend to cause the process pressure, and subsequent process performance, to vary with time.

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